Hadi loyalists in the southern port city reported a gun battle in the central Crater district in which three people were killed, and said they recaptured the airport, which has changed hands several times in several days of fighting.

The Health Ministry, loyal to the Houthi fighters who control the capital, said Saudi-led air strikes had killed 35 people and wounded 88 overnight. The figures could not be independently confirmed.

The Houthi fighters, representing a Shi'ite minority that makes up around a third of Yemen's population, emerged as the most powerful force in the Arabian Peninsula's poorest country last year when they captured the capital Sanaa.

Saudi Arabia has rallied Sunni Muslim Arab countries in an air campaign to support Hadi, who moved to Aden in February and is now in Riyadh after leaving Yemen in the past week. The fighting has brought civil war to a country that was already sliding into chaos and which had been a battlefield for the secret U.S. drone war against al Qaeda.

While the Houthi fighters and their army allies continued to make gains after the air strikes were first launched early on Thursday, they appeared to suffer reversals on Sunday on three fronts - in Aden's northern suburbs, in Dhalea province north of Aden, and the eastern province of Shabwa.

In Shabwa, tribal sources said tribesmen killed 30 Houthis in a battle with the Shi'ite militia and its army allies at a military base. This also could not be independently confirmed.

Saudi-led coalition warplanes struck military targets at airports in the capital Sanaa and in Hodeida, the main Red Sea port.